Bearings are usually employed in pairs and in coaxial arrangements to support a rotating member, e.g., motor shaft. Ideally, the two bearings are located by a stationary member that constrains the two bearings in perfect axial alignment. Real world designs are less than perfect and, therefore, compromise bearing performance.
A widely employed bearing suspension mode involves holding each bearing within a separate housing structure and fitting those housing structures together to approximate a coaxial bearing arrangement. For example, FIG. 7 illustrates a housing H holding bearing B1 and a cap C holding bearing B2, the cap C being fitted to the housing H to support a rotor R between the bearings B1, B2.
There are two main classes of constraints on the packaging of bearings. One constraint relates to the practical limits of manufacturing precision, and another constraint relates to the need to attach and efficiently package items that must rotate.
With respect to the first constraint, although the precision of part forming technologies improves continuously, the state of the art is far from perfect. Furthermore, increased precision usually translates to greater expense, often dissuading a manufacturer from embracing the state of the art processes.
The second constraint is driven by the need to place items (such as a rotor/stator) between bearing pairs. This leads to the use of a two part housing construction. A consequence of multipart housings is that they accumulate unwanted tolerance build-up at each faying or joint surface.
A less widely employed bearing suspension mode is to utilize a single metallic tube to house the bearing pair, and to hang the rotor from one end in cantilever fashion, i.e., an outer rotor design. For example, FIG. 8 illustrates a metallic tube T housing bearings B1, B2, and a rotor R supported by the bearings B1, B2 in cantilever fashion to support an impeller I. However, the metallic tube prevents a high speed magnetic rotor from being packaged between the bearings, i.e., an internal rotor design, because magnetic fields cannot effectively cross a metallic barrier without significant loss of flux density and/or increased heat. Also, there are practical limits to how much mass and length can be cantilevered from a set of high speed bearings. Therefore, such designs tend to be axially short in length.
Thus, a need has developed in the art for an improved arrangement that does not suffer from the above-mentioned drawbacks.